The present invention relates to a production process for a magnetic recording medium used in, for example, a hard disk apparatus.
In recent years, recording density has been considerably increased in the field of magnetic recording, particularly in the case of recording in a hard disk apparatus. A variety of techniques are required for enhancing recording density. One example is a technique for controlling sliding characteristics between a magnetic head and a magnetic recording medium. With respect to magnetic recording media, a protective film formed on a magnetic film, a lubricant, etc. have been continuously developed and improved.
In order to increase recording density, spacing loss must be reduced. To this end, the flying height of a magnetic head is reduced, and therefore, wear resistance, sliding characteristics, and corrosion resistance of a surface of a magnetic recording medium are key factors for evaluating the reliability of the recording medium. In order to reduce such spacing loss, a thin protective film is desirable, having a thickness of, e.g., 100 xc3x85 or less. Thus, there is strong demand for a protective film which is thin and exhibits high toughness, to say nothing of smoothness.
A variety of materials have been proposed for a protective film of a magnetic recording medium. Of these, a protective film predominantly comprising carbon has been employed in consideration of overall characteristics, including film-formability, wear resistance, and sliding characteristics. The protective film predominantly comprising carbon is typically formed through sputtering. However, when a thin protective film; i.e., a protective film as thin as 100 xc3x85 or less, is produced through a conventional sputtering process, the film might have poor wear resistance and poor sliding characteristics.
In order to solve this problem, a plasma CVD method which can provide a protective film predominantly comprising carbon and having higher mechanical strength has been employed. Specific plasma CVD techniques are disclosed in Japanese Laid-Open Patent Application (Kokai) No. 7-73454 and Japanese Patent Publication (Kokoku) No. 7-21858.
When a protective film formed of carbon is produced on a substrate through a conventional plasma CVD method, a carbon film is also deposited on the interior walls of a chamber. When carbon film is exfoliated by, for example, due to stress, carbon dust is generated. If carbon dust is deposited on the carbon film, the surface smoothness of the carbon film is deteriorated, resulting in deterioration of a glide characteristic, which is one of the quality indices of a magnetic recording material; whereas if carbon dust is deposited on a substrate, an undercoat film or a magnetic film is exfoliated, to thereby result in a deterioration of an error characteristic, which is another one of the quality indices for a magnetic recording material. Carbon dust induces anomalous discharge during plasma generation, deteriorating the anti-corrosion characteristic of the formed protective film, to thereby deteriorate the quality of the produced magnetic recording medium. In addition, these defective products must be removed by inspection, and therefore, in mass production, the overall production yield decreases.
Furthermore, anomalous plasma discharge caused by carbon dust hampers constant operation of a film-forming apparatus.
Meanwhile, a conventional plasma CVD method requires interruption of operation and opening of the chamber of a film-forming apparatus in order to clean the chamber for removing carbon deposits. This results in disadvantageously low operation efficiency, in that not only is interruption of the apparatus required, but additional time is needed after cleaning is finished; specifically, for checking the quality of formed carbon film, which might be deteriorated due to exposure of the vacuum apparatus to air.
In view of the foregoing, the present invention provides a production process for a magnetic recording medium, which process solves the above problems.
The present inventors have conducted extensive studies, and have found that the above problems can be solved through application of oxygen plasma to transform carbon deposits on the inner walls of a chamber. The present invention has been accomplished on the basis of this finding.
Accordingly, a first embodiment of the present invention is directed to a production process for a magnetic recording medium having a non-magnetic substrate, a non-magnetic undercoat film, a magnetic film, and a protective film predominantly comprising carbon, the protective film being formed through a plasma CVD method employing a carbon-containing gas as a source, which process comprises applying an oxygen plasma to carbon deposits on the inner walls of a chamber or to carbon present in the chamber, for inducing conversion of carbon.
A second embodiment of the present invention is directed to a production process according to the first embodiment, wherein the pressure in the chamber during oxygen plasma discharge is at least about 3 Pa and less than about 150 Pa.
A third embodiment of the present invention is directed to a production process according to embodiments 1 or 2, wherein the amount of residual oxygen in a CVD chamber is decreased to a pressure of about 2.5xc3x9710xe2x88x923 Pa or less during the time between completion of oxygen plasma discharge and formation of another protective film.
A fourth embodiment of the present invention is directed to a production process according to embodiment 1, wherein, after completion of oxygen plasma discharge, residual oxygen in the chamber is substituted by a process gas.
A fifth embodiment of the present invention is directed to a production process according to the fourth embodiment, wherein substitution of the process gas for residual oxygen in the chamber is carried out for at least one second and less than five seconds.
A sixth embodiment of the present invention is directed to a production process according to any one of embodiments 1 to 5, wherein feed of oxygen gas is stopped before completion of oxygen plasma discharge, and the plasma discharge is maintained by pressure of residual oxygen in the chamber.
A seventh embodiment of the present invention is directed to a production process according to the sixth embodiment, wherein feed of oxygen gas is stopped about 0.5 to 2 seconds before completion of oxygen plasma discharge and the plasma discharge is maintained by pressure of residual oxygen in the chamber.
The application of oxygen plasma to carbon deposits on the inner walls of the chamber or to carbon present in the chamber for transformation will next be described. Oxygen plasma formed from fed oxygen gas comprises oxygen ions and oxygen radicals produced through excitation of oxygen molecules. After formation of a protective film predominantly comprising carbon, carbon is deposited on an exposed surface such as an electrode plate disposed on the inner walls of the chamber or a shield in the chamber. Flaking of the deposited carbon generates carbon dust. Oxygen ions or oxygen radicals collide with carbon deposits and carbon dust, to thereby form gases such as carbon monoxide and carbon dioxide, which gases are evacuated. Thus, carbon deposits on the inner walls of the chamber or carbon present in the chamber are removed. This mechanism has a cleaning effect and the process is advantageously operated such that residual oxygen is present where the oxygen plasma discharge is completed until the next cycle.
The above-described problems can be solved by means of the cleaning effect, with the result that a magnetic recording medium of high quality can be produced at high yield and a film-forming apparatus can be run at an improved operation rate.